For this exercise you need to remember that the circumference of a circle can be calculated with this formula:
[tex]C=2\pi r[/tex]
Where "r" is the radius of the circle.
In this case, you know that the circumference of the circle is:
[tex]C=21.2ft[/tex]
Then, you can substitute this value into the formula and solve for "r". This is:
[tex]\begin{gathered} C=2\pi r \\ 21.2ft=2\pi r \\ \\ \frac{21.2ft}{2\pi}=r \\ \\ r\approx3.37ft \end{gathered}[/tex]
You can find the diameter by multiplying the radius by 2. Then, this is:
[tex]\begin{gathered} d=(2)(3.37ft) \\ d\approx6.74ft \end{gathered}[/tex]
The answers are:
[tex]\begin{gathered} d\approx6.74ft \\ r\approx3.37ft \end{gathered}[/tex]
